1. Field of the Invention
The invention relates to friction clutches. In particular the invention pertains to dual friction clutches for connecting a power source output shaft alternately to input shafts of a motor vehicle transmission.
2. Description of the Prior Art
Conventional automotive dry clutch systems are supported directly on the engine crankshaft distant from the center of mass of the system. The mass of the clutch system is cantilevered and subject to bending displacement relative to the centerline of the crankshaft. As the crankshaft rotates, the mass of the clutch system is subject to orbiting motion about the true centerline of the crankshaft. The resulting orbiting radius from the crankshaft axis and the clutch mass together induce a first order forced vibration in the powertrain, which further increases crankshaft deflection and increases load on the system.
Misalignment of the engine crankshaft centerline relative to the transmission input shaft centerline can cause the surfaces of the friction discs of the clutch to wear irregularly in compliance with the misalignment. Misalignment of the clutch mass relative to the crankshaft during initial installation also contributes to the problem.
U.S. Publication US2003/0066730, dated Apr. 10, 2003, describes an example of a clutch assembly installed between a drive unit and a transmission having a transmission input shaft to transmit torque between the drive unit and the transmission. The clutch and a portion of the clutch actuation system hardware are supported on an engine crankshaft. The clutch mass is cantilevered a substantial distance from the crankshaft support across a space occupied by the clutch and its actuators.
Automotive torque converter systems conventionally are secured to the engine crankshaft with a compliant or flexible member, which allows axial and bending displacement, and are supported on the transmission by a single bushing or bearing. The partially supported cantilevered mass of the torque converter, due to bending or flexing and whirl of the crankshaft rotates in an orbiting motion about the true centerline of the crankshaft. The resulting orbit radius and torque converter mass induce a first order vibration in the powertrain, which increases the crankshaft deflection and resulting loads. But misalignment of the engine crankshaft centerline relative to the transmission input shaft centerline is accommodated by compliance within a compliant, flexible member located in a torque-transmitting path between the crankshaft and torque converter. Misalignment of the torque converter mass relative to the crankshaft during installation and misalignment of the transmission support relative to the engine crankshaft centerline contribute to the vibration.
Instead, a powertrain assembly for transmitting torque from an engine to two transmission input shafts may include two flywheels, each associated with one of the input clutches. In this case, there is need to support one of the clutches and the corresponding flywheel on the engine crankshaft. The other clutch and its corresponding flywheel can be supported on the transmission housing. This arrangement would eliminate transient effects that induce vibrations caused by misalignment of the crankshaft axis and the axis of rotation that is supported on the transmission housing. This structural arrangement would eliminate entirely the cantilevered support currently provided to the clutch masses.